Well-Known Member

I set up a 10.5" AR pistol recently (5.56/.223) as an 80% build (this is not my first 80%), with a factory upper and upon testing it, I got about 20 rounds through it before I started getting light primer strikes (light enough to see a faint mark, but not strong enough to even hear any click of the trigger/hammer) with every round the gun would chamber. It shoots the first shot that I manually chamber with the charging handle or bolt release, but every subsequent shot has the aforementioned issue. Here are the things I've tried:
- Complete de-lubing and light lubing.
- Different BCG.
- Holding the bolt catch release down while shooting (this was an issue on a previous build that necessitated the slight filing-down of the catch).
- Using the forward-assist button.
- Different types of ammo.
^^^All of these have had ZERO effect on the issue in question. Again, if I manually cycle the BCG, that round will fire without issue. So, overall, when it cycles, it will successfully load a new round and eject the old one, but the new chambered round will receive a light primer strike and will not be set off.

Has anyone encountered a similar issue? From those I've talked with already it sounds like either a hammer/hammer spring issue or a gas issue. How do I go about troubleshooting this more?

Pain in the neck.Gold SupporterBronze Supporter

If the primer has a small mark then it should be going into battery.
You said there is no click when you pull the trigger?

That sounds like the trigger is not resetting?

So. With the gun made safe. And the hammer dropped. Pull and hold the trigger.
Use the charging handle to pull the carrier back and supposedly cock the hammer.
All the time holding back the trigger.
Let the bolt go forward. When the bolt is forward back in battery. Let off the trigger.
You should hear an audible click.
Then pull the trigger. You should here the hammer fall.

Do this five or so times to make sure the hammer catches wile the trigger is pulled.
Just as it would have to do when you shoot your second or subsequent shots.

Well-Known Member

If the primer has a small mark then it should be going into battery.
You said there is no click when you pull the trigger?

That sounds like the trigger is not resetting?

So. With the gun made safe. And the hammer dropped. Pull and hold the trigger.
Use the charging handle to pull the carrier back and supposedly cock the hammer.
All the time holding back the trigger.
Let the bolt go forward. When the bolt is forward back in battery. Let off the trigger.
You should hear an audible click.
Then pull the trigger. You should here the hammer fall.

Do this five or so times to make sure the hammer catches wile the trigger is pulled.
Just as it would have to do when you shoot your second or subsequent shots.

Click to expand...

Interesting, something is off, get this: I did exactly what you said and when I let off the trigger... nothing, however then I grabbed the trigger and pushed it forward slightly then I heard the click! So what does this sound like to you? The trigger position is off or something shifted? This was an experimental build for me with a cheap plastic lower that I was given and "finished" with a Dremel. So maybe something is screwed up or needs modding. Thoughts?

Pain in the neck.Gold SupporterBronze Supporter

Look down on your trigger group with the upper off the gun.
Cock the hammer with your thumb wile holding the trigger. Then let off the trigger and see if the disconector lets go of the hammer and hands contron over to the trigger sear?
It sounds like the hook on the disconector is not letting go of the hammer when you let go of the trigger.

Easiest thing? A bad trigger disconector. Or some smoothing.

Or the pin holes not drilled in the wright place?
I.E. Bad trigger geometry.

If it was a trigger/hammer sear not catching when the disconector handed the hammer off to the trigger sear. You would hear the hammer drop when you let off the trigger in my earlier test.

Well-Known Member

Look down on your trigger group with the upper off the gun.
Cock the hammer with your thumb wile holding the trigger. Then let off and see if the disconector lets go off the hammer and hands contron over to the trigger sear?
It sounds like the hook on the disconector is not letting go of the hammer when you let go of the trigger.

Easiest thing? A bad trigger disconector. Or some smoothing.

Or the pin holes not drilled in the wright place?
I.E. Bad trigger geometry.

If it was a trigger/hammer sear not catching when the disconector handed the hammer off to the trigger sear. You would hear the trigger drop when you let off the trigger in my test.

Click to expand...

I feel confident in the drill holes.

How do I check the disconnector?

So you're saying that it isn't the trigger/hammer sear not catching, so that's ok?

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